Semiconductor production device ceramic plate

ABSTRACT

This invention has its object to provide a ceramic board which, when used as a heater, heats a silicon wafer uniformly throughout and, hence, does not damage the wafer and, when used as an electrostatic chuck, provides a sufficient chucking force.  
     This invention provides a ceramic board for semiconductor manufacture apparatuses comprising a ceramic substrate and a semiconductor wafer mounted thereon directly or supported indirectly at a fixed distance from its surface,  
     wherein the surface of said ceramic substrate, where said semiconductor wafer is to be mounted or supported, is controlled to a flatness of 1 to 50 μm over a measurement range of [(diametric end-to-end length)−10 mm].

TECHNICAL FIELD

[0001] The present invention relates essentially to a ceramic board forthe electrostatic chuck, wafer prover and other implements to be used inthe manufacture of semiconductor apparatuses and more particularly to aceramic board for semiconductor manufacture apparatuses which is capableof supporting large-sized semiconductor wafers and dose not adverselyaffect silicon wafers.

BACKGROUND ART

[0002] Semiconductors are extremely important articles of commercerequired in various industries, and typically semiconductor chips aremanufactured by the technology which comprises slicing a silicon singlecrystal to prepare a silicon wafer having a predetermined thickness andconstructing various circuits and other components on said wafer.

[0003] In the above process for manufacturing a semiconductor chip,various semiconductor production implements each based on a ceramicboard, such as the electrostatic chuck, hot plate, wafer prover andsusceptor, are used on many occasions.

[0004] Regarding such implements for semiconductor manufactureapparatuses, the ceramic boards for use in these applications aredescribed in JP Kokoku 2587289 and Japanese Kokai PublicationHei-10-72260, for instance.

[0005] The ceramic boards disclosed in the above patent literature andother publications are invariably available only within the size rangeof not over about 6 inches (150 mm) in diameter and not less than 8 mmin thickness.

[0006] However, the recent trend toward increase in the size of asilicon wafer has led to a demand for ceramic boards as large as 8inches or more in diameter.

[0007] Meanwhile, in the process for manufacturing silicon wafers,heating procedures require the use of a heater having a heating elementembedded in a ceramic substrate and for achieving an improvedtemperature response or follow-up efficiency through a reduction in heatcapacity, the thickness of the ceramic board must be reduced to lessthan 8 mm.

[0008] On the other hand, there has been disclosed a ceramic boardhaving a wafer-mounting surface controlled to a roughness value of notmore than Rmax=2 μm (Japanese Kokai Publication Hei-7-280462).

[0009] However, the manufacture of a hot plate, an electrostatic chuckor the like using such a large and thin ceramic board was found toinvolve various problems, for example the creation of a temperaturegradient in the silicon wafer placed thereon and consequent destructionof the wafer by thermal shock or the failure to generate a sufficientchucking force despite the reduced surface roughness and the consequentnon-uniformity of wafer temperature.

SUMMARY OF THE INVENTION

[0010] The inventors of the present invention did much research in theabove state of the art and found that troubles such as destruction ofthe silicon wafer, non-uniformity of wafer temperature due to aninsufficient chucking force, and the unevenness of silicon wafertemperature which occurs in a heating mode where the wafer is heated insuspension at a certain distance from the surface of the ceramic boardare all caused by the presence of an undulation in the surface of theceramic substrate. Further investigations revealed that the abovetroubles can be overcome by reducing the surface undulation of a ceramicsubstrate so that the surface will fall within a certain range offlatness. The present invention has been developed on the basis of theabove finding.

[0011] The ceramic board for semiconductor manufacture apparatusesaccording to a first aspect of the present invention, therefore,comprises a ceramic substrate and semiconductor wafer directly mountedor indirectly supported at a fixed distance from its surface,

[0012] wherein the surface of a ceramic substrate, where saidsemiconductor wafer is to be mounted or supported, is controlled to aflatness of 1 μm to 50 μm over a measurement range of [(the diametricend-to-end length of the substrate)−10 mm].

[0013] The ceramic board for semiconductor manufacture apparatusesaccording to a second aspect of the present invention comprises aceramic substrate and a conductor layer disposed internally or on asurface thereof,

[0014] wherein said surface is controlled to a flatness of 1 to 50 μmover a measurement range of [(said diametric end-to-end length)−10 mm].

[0015] In the ceramic boards for semiconductor manufacture apparatusesaccording to said first and second aspects of the present invention,said flatness is preferably 1 to 20 μm.

[0016] Flatness is a concept quite different from roughness. Thus,whereas flatness is pertinent to the macroscopic undulation of asurface, roughness is a marker of microscopic irregularities of asurface.

[0017] Therefore, if the roughness of a surface is Rmax=20 μm, it is notnecessarily true that the flatness of the surface is 20 μm. Flatness asso referred to in this specification is defined as the head between thehighest point and the lowest point within a measurement range (FIG. 4and FIG. 5).

[0018] Diametric end-to-end length as so referred to in thisspecification means the length of any imaginary straight line passingthrough the center of a ceramic substrate from one end to thediametrically opposite end on its periphery. Thus, when the ceramicsubstrate is circular or disk-shaped, the diametric end-to-end length isthe diameter of the disk, and when the ceramic substrate is elliptic inplan view, the diametric end-to-end length means both the dimension ofthe major axis and that of the minor axis. In the present invention, themeasurement range of [(diametric end-to-end length)−10 mm] isestablished in two directions, i.e. along X- and Y-axes, and whicheverlarger of the two measured values is taken as the flatness of theceramic board.

[0019] In the present invention, the flatness is measured over thesurface area exclusive of the area to be occupied by a silicon wafer,i.e. the marginal area within 5 mm from the periphery of the ceramicsubstrate. Thus, the [(diametric end-to-end length)−10 mm] is themeasurement area.

[0020] In the ceramic board for semiconductor manufacture apparatuses,said ceramic substrate is in the form of a disk with a diameter inexcess of 150 mm.

[0021] The reason is as follows. When the diameter of the disk is notmore than 150 mm, the ceramic board and the wafer to be mounted thereonare intrinsically small enough to insure a comparatively uniformtemperature distribution. Therefore, the problems to be solved by theinvention, namely the risks for breakage of the silicon wafer andnon-uniformity of the wafer temperature, do not exist from thebeginning:

[0022] The ceramic substrate in the present invention is preferably notless than 200 mm in diameter and most preferably not less than 300 mm indiameter, for said risks for breakage of silicon wafers andnon-uniformity of the wafer temperature are high when the ceramicsubstrate is more than 200 mm in diameter.

[0023] The ceramic substrate mentioned above preferably comprisesnitride ceramics and more preferably comprises aluminum nitride, siliconnitride and/or boron nitride.

[0024] Preferably, said ceramic substrate contains more than 50 weight %of aluminum nitride.

[0025] The conductor layer disposed internally of the ceramic substrateis preferably formed as at least one layer in the center in thicknessdirection thereof or in an offset position displaced from said centertoward the surface thereof,

[0026] said surface being opposite to the surface where a semiconductorwafer is to be mounted or supported.

[0027] In addition, the conductor layer is preferably formed on thesurface of the ceramic substrate,

[0028] said surface being opposite to the surface where a semiconductorwafer is to be mounted or supported.

[0029] The ceramic boards for semiconductor manufacture apparatusesaccording to the first and second aspects of the present inventionpreferably comprises

[0030] a conductor layer formed on the surface of said ceramic substrateand

[0031] a semiconductor wafer mounted on said conductor layer,

[0032] said ceramic board functioning as a wafer prover.

[0033] Furthermore, the conductor layer disposed internally of saidceramic substrate preferably comprises at least one layer formed in anoffset position displaced from the center in thickness direction thereoftoward the surface where a semiconductor wafer is to be mounted orsupported.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a schematic bottom view showing a ceramic heater as anembodiment of the ceramic board for semiconductor manufactureapparatuses according to the present invention.

[0035]FIG. 2 is a partial section view, on exaggerated scale, of theceramic board of FIG. 1.

[0036]FIG. 3(a) to (e) are schematic cross-section views illustratingthe flow of manufacture of the ceramic board for semiconductormanufacture apparatuses in Example 1.

[0037]FIG. 4 is a diagrammatic representation of the surface flatness ofthe ceramic board for semiconductor manufacture apparatuses asfabricated in Example 1.

[0038]FIG. 5 is a diagrammatic representation of the surface flatness ofthe ceramic board for semiconductor manufacture apparatuses asfabricated in Example 2.

[0039]FIG. 6(a) to (d) are schematic cross-section views illustratingthe flow of manufacture of the ceramic board for semiconductormanufacture apparatuses in Example 3.

[0040]FIG. 7(e) to (g) are schematic cross-section views illustratingthe flow of manufacture of the ceramic board for semiconductormanufacture apparatuses in Example 3.

[0041]FIG. 8 is a schematic section view showing the ceramic boardobtained in Example 3 as mounted on a support base.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]3 ceramic substrate

[0043]5 guard electrode

[0044]6 ground electrode

[0045]7 groove

[0046]8 air suction hole

[0047]10 ceramic heater

[0048]11 ceramic substrate

[0049]12 conductor layer (heating element)

[0050]13 terminal pin

[0051]14 (14 a to 14 i) blind hole

[0052]15 through hole

[0053]16 support pin

[0054]17 metal cover layer

[0055]19 silicon wafer

[0056]26, 27 plated-through holes

[0057]28 recesses

[0058]31 support

[0059]32 nozzle port for ejecting a cooling medium

[0060]33 suction port

[0061]34 nozzle port for injecting a cooling medium

[0062]41 heating element

[0063]101 wafer prover

[0064]410 metal cover layer

[0065]29, 290, 291 external terminal pins

DETAILED DESCRIPTION OF THE INVENTION

[0066] The ceramic board for semiconductor manufacture apparatusesaccording to the first aspect of the present invention comprises aceramic substrate having a surface on which a semiconductor wafer is tobe directly mounted or indirectly supported at a fixed distance fromsaid surface, in which the degree of flatness of said surface of theceramic substrate on which a semiconductor wafer is to be directlymounted or indirectly supported (hereinafter referred to sometimes aswafer-mounting surface) is 1 to 50 μm over a measurement range of[(diametric end-to-end length)−10 mm].

[0067] The ceramic board according to the second aspect of the presentinvention comprises a ceramic substrate and a conductor layer disposedinternally or on a surface of said ceramic substrate, in which thedegree of flatness of said surface of the ceramic substrate on which asemiconductor wafer is to be directly mounted or indirectly supported is1 to 50 am over a measurement range of [(diametric end-to-end length)−10mm].

[0068] In the ceramic boards for semiconductor manufacture apparatusesaccording to said first and second aspects of the present invention, thewafer-mounting surface of the ceramic substrate is controlled to aflatness value within a specified range as mentioned above. Therefore,with a hot plate, electrostatic chuck or the like manufactured usingeither ceramic board as the constituent material, the silicon wafer canbe heated uniformly throughout to prevent the breakage of the wafer bythermal shock and, at the same time, can be attracted with a sufficientforce of attraction and set securely in position.

[0069] Furthermore, in the mode of use where the wafer is supported bymeans of support pins or the like and heated as such with a clearance of50 to 500 μm maintained between the wafer and the ceramic substrate, thespan of said clearance can be made substantially uniform so that theuneven distribution of wafer temperature can be prevented.

[0070] The ceramic board according to the first aspect of the inventionis different from the ceramic board according to the second aspect ofthe invention only in the restriction on conductor layer and otherwiseis identical in construction to the latter ceramic board. Therefore, inthe following description of the ceramic boards according to the firstand second aspect of the invention, both boards will be collectivelyreferred to as the ceramic board except in cases in which a distinctionmust be made between the two boards.

[0071] The mode of application of the ceramic board of the invention isnot restricted to the application in which a silicon wafer is mounteddirectly or indirectly thereon for various kinds of processing (forexample, formation of circuits).

[0072] The ceramic board for semiconductor manufacture apparatusesaccording to the present invention is not restricted to any particularkind insofar as it is used for the manufacture of implements forsemiconductor manufacture apparatuses, but includes the electrostaticchuck, wafer prover, susceptor, and hot plate (ceramic heater).

[0073] The implements as so referred to in this specification includeinstruments to be used in the inspection stage.

[0074] In the mode of application of the ceramic board for semiconductormanufacture apparatuses according to the invention as a ceramic heater,if the flatness of said wafer-mounting surface exceeds 50 to m over ameasurement range of [(diametric end-to-end length)−10 mm], the wafertemperature will not increase sufficiently regardless of whether thewafer is directly mounted or supported at a fixed distance from thewafer-mounting surface.

[0075] Thus, even if it is attempted to heat the wafer mounted on such aceramic board, the wafer will not be heated to a temperature of, say,200° C. because its contact with the ceramic board is either pointcontact or line contact. On the other hand, even if it is attempted toheat the wafer supported with pins at a fixed distance from the surfaceof such a ceramic board, the excessive variation in the clearancebetween the wafer and the heating surface of the ceramic board willbring the wafer into local contact with the ceramic board, with theresult that the wafer cannot be properly heated.

[0076] Furthermore, if the flatness value of the wafer-mounting surfaceof the ceramic board is greater than 20 μm over a measurement range of[(diametric end-to-end length)−10 mm], a gap will be formed between thesilicon wafer and the wafer-mounting surface so that a large temperaturegradient is at times produced in the wafer. Moreover, even if it isattempted to heat the wafer supported with support pins or the like at afixed distance from the ceramic substrate, viz. without contact, theexcessively large variation in distance between the silicon wafer andthe wafer-mounting surface of the ceramic substrate similarly produces atemperature gradient in the wafer at times.

[0077] On the other hand, when said flatness is less than 1 μm in themode of use where a silicon wafer is directly mounted on the ceramicboard, the wafer comes into intimate contact with the wafer-mountingsurface of the ceramic substrate so that the silicon wafer becomesunreleasable due to atmospheric pressure.

[0078] When said flatness is greater than 50 μm in the mode of use ofthe ceramic board as an electrostatic chuck, attraction of the siliconwafer toward the ceramic substrate causes deformation of the wafer inconformity with the surface undulation of the ceramic board, resultingin cracking of the wafer at times. On the other hand, when said flatnessis less than 1 μm, the silicon wafer comes into intimate contact withthe wafer-mounting surface so that the wafer becomes unreleasable due toatmospheric pressure. Although the electrostatic chuck is used in avacuum, the atmospheric pressure must be reinstated for transfer of thewafer and, then, the trouble of wafer unreleasability occurs.

[0079] If said flatness value is greater than 50 μm in the mode of useof the ceramic board for semiconductor manufacture apparatuses(hereinafter referred to briefly as ceramic board) as a wafer prover,gaps will be created between the silicon wafer mounted and the surfaceof the ceramic substrate, and when the tester pin is depressed in thearea corresponding to such a gap, the silicon wafer deforms inconformity with the surface undulation of the ceramic board and becomesdamaged.

[0080] On the other hand, setting said flatness value at less than 1 μmdoes not make sense economically because there is already a variation ofabout 1 μm in the thickness of the chuck top conductor layer itself.

[0081] The preferred value of said flatness is 1 to 20 μm. Thus, whenthe ceramic board of the present invention is used as a ceramic heater,no remarkable temperature gradient is produced in the silicon wafer.Also, when it is used as an electrostatic chuck, the variation indistance between the silicon wafer and the electrostatic chuckelectrodes is small enough so that a sufficient chucking effect isproduced and, moreover, the silicon wafer can be easily released fromthe ceramic substrate after use. When said ceramic board is applied to awafer prover, the deformation of the silicon wafer is so small that theincidence of wafer damage can be almost completely inhibited.

[0082] The wafer prover is an instrument for use in a conduction testwhich comprises pressing tester pins against a silicon wafer placedthereon.

[0083] In the ceramic heater according to the present invention, theshape of said nitride ceramic substrate is not particularly restrictedbut may for example be elliptic in plan view but a circular board ordisk is preferred. When the nitride ceramic board is a disk, itsdiameter is preferably over 150 mm, more preferably over 200 mm, andstill more preferably over 300 mm. This is because the diameters ofsemiconductor wafers in popular use today are not less than 8 inches(200 mm) and the next-generation semiconductor wafers will mostly beavailable in the diameter range of not less than 12 inches (300 mm).

[0084] Moreover, if the diameter of the ceramic substrate is less than200 mm, the compatible wafer will also be so small in diameter that itwill be readily heated uniformly and even if the flatness value of theceramic substrate is large, the wafer will be ready to follow thesurface topology of the ceramic substrate so that no reduction inchucking force will take place. Thus, such a ceramic substrate does nothave the problems to be solved by the present invention.

[0085] Thus, the effect of the present invention is particularlyremarkable when the ceramic board diameter is not less than 200 mm.

[0086] The thickness of said ceramic board is preferably not over 50 mm,for such a board does not easily undergo warp at high temperature. Themore preferred thickness is less than 8 mm. This is because, when theboard thickness is 8 mm or greater, the heat capacity of the ceramicboard is increased so that when the heating and cooling cycle iscontrolled with a temperature control means, the temperature follow-upefficiency is adversely affected.

[0087] The thickness of the ceramic substrate is more preferably notgreater than 5 mm. If the thickness exceeds 5 mm, the heat capacity ofthe substrate will be increased to adversely affect temperaturecontrollability and temperature uniformity of the wafer-mounting surfaceat times.

[0088] For the ceramic board of the present invention, it is preferableto use ceramics having a Young's modulus of not less than 280 GPa overthe temperature range of room temperature to 800° C. Such ceramics arenot particularly restricted but include nitride ceramics, among others.If Young's modulus is less than 280 GPa, the amount of warp at hightemperature will be too large to be controlled even if a reinforcingconductive layer is provided.

[0089] The nitride ceramics mentioned above may be any of aluminumnitride, silicon nitride, boron nitride and other ceramics but the useof aluminum nitride is preferred. The most preferred is a ceramic boardcomprising aluminum nitride of more than 50 weight %. The other ceramiccomponents which can be used include alumina sialon, and the like.

[0090] The Young's modulus of said ceramic substrate can be controlledby using a blend or a laminate of two or more different ceramics orincorporating oxides of metals, such as alkali metals, alkaline earthmetals, and rare earth metals, carbon, etc. The preferred alkali metalsor alkaline earth metals are Li, Na, Ca and Rb, and the preferred rareearth metal is Y. The carbon may be whichever of amorphous carbon andcrystalline carbon. The carbon content is preferably 200 to 5000 ppm. Byusing carbon within this range, the ceramic board can be blackened.

[0091] The ceramic board of the present invention preferably has noporosity, i.e. 0%, or a porosity of not over 5%. Thus, when the porosityis controlled to less than 5%, the resulting closed-cell structureinsures a high insulation resistance and the board does not warp even ata temperature not less than 200° C., with the surface flatness at roomtemperature being retained even at high temperature.

[0092] The maximum pore diameter of the ceramic substrate is preferably0 or not more than 50 μm. When the pore size is 0 or not more than 50μm, the board does not warp even at 200° C. or up and the flatness atroom temperature can be maintained at high temperature.

[0093] The porosity mentioned above is measured by the method ofArchimedes. To measure the maximum pore diameter, 5 samples are preparedand respectively photographed in 10 positions under an electronmicroscope and the diameters of the largest pores (50 pores) in eachshot are averaged.

[0094] When a conductor layer is to be formed internally or on a surfaceof said ceramic substrate, the conductor layer preferably comprises ametal or conductive ceramic paste, and at least a single layer ispreferably disposed in the center in thickness direction of the ceramicsubstrate or in an offset position displaced from the center toward thesurface opposite to the wafer-mounting surface. As an alternative, theconductor layer may be formed on the surface opposite to thewafer-mounting surface.

[0095] When said conductor layer is to constitute the chuck topelectrodes of a wafer prover, the particular conductor layer is formedon the surface of the ceramic substrate on the side on which asemiconductor wafer is mounted. The semiconductor wafer is mounted onthis conductor layer.

[0096] In addition, the ceramic substrate may be internally formed witha conductor layer functioning as a guard electrode and a groundelectrode.

[0097] In case the conductor layer is to constitute electrodes (staticelectrodes) of an electrostatic chuck, it is formed internally of theceramic substrate but closer to the wafer-mounting surface.

[0098] Since warp results in extension of the ceramics in the regionfarthest from the wafer-mounting surface, this warp is precluded bydisposing a conductor layer as a reinforcement in the region of saidextension, whereby the silicon wafer can be protected against damage.Then, in the mode of use as a wafer prover, an accurate conduction testcan be carried out, while in the case of an electrostatic chuck, thereduction in the force of attraction acting on the silicon wafer can beprevented.

[0099] The configuration of said conductor layer may for example be aplane, several divisions of a plane, a vortex, concentric circles, or agrid.

[0100] The thickness of said conductor layer is preferably about 1 to 50μm. If the layer is less than 1 μm thick, no reinforcing effect will beobtained. If the thickness is greater than 50 μm, warp of the wholeceramic board and a reduction in flatness of the wafer-mounting surfacewill be induced.

[0101] The conductor layer may for example be comprised of a sinteredmetal, non-sintered metal, or a sintered conductive ceramic material.

[0102] The raw material of said sintered metal or non-sintered metal mayfor example be a high-melting metal. The high-melting metal mentionedjust above includes tungsten, molybdenum, nickel and indium. Thesemetals may be used singly or in a combination of two or more species.

[0103] The conductive ceramic material mentioned above includes thecarbide of tungsten or molybdenum.

[0104] The conductor layer, when it is formed internally of the ceramicsubstrate, may be utilized as, for example, a heating element, a guardelectrode, a ground electrode and/or static electrodes and, when it isformed on the surface of the ceramic substrate, can be utilized as, forexample, a heating element or chuck top electrodes.

[0105] Furthermore, as mentioned above, the ceramic substrate may beinternally formed with a plurality of conductor layers adapted tofunction as, for example, a heating element, a guard electrode, a groundelectrode, etc., respectively.

[0106] The ceramic board provided with a heating element and others inthis manner can be used as, for example, a hot plate (ceramic heater),an electrostatic chuck, or a wafer prover.

[0107]FIG. 1 is a schematic bottom view of a ceramic heater as anapplication of the ceramic board for semiconductor manufactureapparatuses according to the present invention and FIG. 2 is a schematicpartial section view, on exaggerated scale, of the same ceramic heater.

[0108] A ceramic substrate 11 is provided in the form of a disk and aconductor layer (heating element) 12 is formed in a pattern ofconcentric circles on the bottom surface of said ceramic substrate 11for heating the whole wafer-mounting surface to a uniform temperature.

[0109] The conductor layer 12 pattern comprises a plurality ofconcentric circles with each set of two neighboring circles constitutinga single conductor line which is connected, at ends, to an input and anoutput terminal pin 13. In the area close to the center of the pattern,through holes 15 are formed for accepting support pins 16. In addition,blind holes 14 a to 14 i are formed for accepting temperature probes.

[0110] As shown in FIG. 2, said support pins 16 are adapted to support asilicon wafer 19 and to raise and lower it with respect to the ceramicboard surface so that the wafer 19 may be delivered to a transfermachine (not shown) or received from the like transfer machine.

[0111] The conductor layer 12 as the heating element may be disposedinternally in the center in thickness direction of the ceramic substrate11 or in an offset position displaced from the center toward thewafer-mounting surface.

[0112] In the above ceramic heater, the conductor layer 12 functions notonly as a mechanical reinforcement but also as a heating element.

[0113] For providing said conductor layer 12 either internally or on thesurface of the ceramic substrate, a conductive paste containing a metalor conductive ceramic powder is preferably employed.

[0114] Thus, the procedure for constructing a conductor layer internallyof the ceramic substrate comprises forming a conductor paste layer on agreen sheet, laminating one or more green sheets thereon and baking thelaminate. On the other hand, the procedure for constructing a conductorlayer on the surface generally comprises fabricating a ceramicsubstrate, forming a conductor paste layer on the surface of thesubstrate and sintering it.

[0115] The conductor paste mentioned above is not particularlyrestricted but is preferably a paste containing a resin, a solvent, athickener, etc. in addition to the metal or conductive ceramic powdernecessary for electrical conductivity.

[0116] The preferred metal powder for this purpose includes powders ofnoble metals (gold, silver, platinum, palladium), lead, tungsten,molybdenum and nickel. These may be used alone or in a combination oftwo or more species. These metals are more or less hardly oxidizable andhave sufficient resistance to generate heat.

[0117] The conductive ceramic powder includes a powder of tungstencarbide or molybdenum carbide. These powders can be used singly or in acombination of two or more species.

[0118] The preferred particle diameter of said metal or conductiveceramic powder is 0.1 to 100 μm. If the powder is finer than 0.1 μm, itwill be ready to be oxidized. On the other hand, if the limit of 100 μmis exceeded, the powder will not be easily sintered and the resistancevalue will be increased.

[0119] The metal powder mentioned above may be spherical or flaky. Amixture of spherical and flaky powders may also be employed.

[0120] When the metal powder comprises flaky particles or a mixture ofspherical and flaky particles, the metal oxide added is held moreeffectively between the metal particles, with the consequent advantagethat a firmer adhesion can be realized between the conductor layer 12and the nitride ceramics and that the resistance value can be increased.

[0121] The resin for use in the conductor paste includes epoxy resin andphenolic resin. The solvent may for example be isopropyl alcohol. Thethickener may for example be cellulose.

[0122] As mentioned above, the conductor paste is preferably a pasteprepared by adding metal oxides to the starting metal powder so that theconductor layer 12 will be a sintered body composed of the metal andmetal oxide. Thus, by sintering the metal oxide together with the metalpowder, an intimate bond can be realized between the substrate nitrideceramics and the metal powder.

[0123] It has not fully been clarified as yet why incorporation of saidmetal oxide results in an improved adhesion to the nitride ceramics, butit may be suggested that since both the surface of the metal particlesand that of the nitride ceramics have been slightly oxidized and theresulting oxide films are integrally sintered together with theintermediary of the metal oxides added, thus causing an intimateadhesion of the metal powder to the nitride ceramics.

[0124] The metal oxide mentioned above is preferably at least one memberselected from the group consisting of lead oxide, zinc oxide, silica,boron oxide (B₂O₃), alumina, yttria and titania.

[0125] These oxides are capable of improving the adhesion between themetal powder and nitride ceramics without increasing the resistancevalue of the conductor layer 12.

[0126] The proportions of said lead oxide, zinc oxide, silica, boronoxide (B₂O₃), alumina, yttria and titania in each 100 weight parts ofthe total metal oxide are 1 to 10 (weight parts; the same applies below)for lead oxide, 1 to 30 for silica, 5 to 50 for boron oxide, 20 to 70for zinc oxide, 1 to 10 for alumina, 1 to 50 for yttria, and 1 to 50 fortitania. The total of these oxides is preferably not more than 100weight parts.

[0127] By adjusting the amount of the oxide within the above range, theadhesion to nitride ceramics, in particular, can be improved.

[0128] The addition amount of said metal oxide relative to the metalpowder is preferably not less than 0.1 weight % and less than 10 weight%. Moreover, the area resistivity of a conductor layer 12 formed from aconductor paste of such composition is preferably 1 to 45 mΩ/□.

[0129] If the area resistivity exceeds 45 mΩ/□, the generation of heatwill be too great in relation to the level of voltage applied so thatthe amount of heat can hardly be controlled in the case of a ceramicsubstrate 11 carrying the conductor layer 12 on the surface. If theaddition amount of said metal oxide exceeds 10 weight %, the arearesistivity will exceed 50 mΩ/□, so that the excessively increased heatgeneration makes temperature control difficult and the uniformity oftemperature distribution will be sacrificed.

[0130] When the conductor layer 12 is formed on the surface of theceramic substrate 11, the surface of the conductor layer 12 ispreferably provided with a metal cover layer 17 as illustrated in FIG. 2for preventing oxidation of the sintered metal and consequent change inresistance value. The thickness of the metal cover layer thus formed ispreferably 0.1 to 10 μm.

[0131] The metal for use in the formation of said metal cove-layer isnot particularly restricted only provided that it is a non-oxidizablemetal but may for example be gold, silver, palladium, platinum ornickel. These metals can be used alone or in a combination of two ormore species. Among the metals mentioned above, nickel is particularlypreferred.

[0132] Where necessary, in accordance with the present invention,thermocouples may be embedded in the ceramic board. This is because bymeasuring the temperature of the heating element with the thermocouplesand varying the voltage and current values based on the temperaturedata, the heater temperature can be controlled.

[0133] The size of junctions of the conductors of the thermocouple ispreferably equal to the diameter of each conductor or larger but notlarger than 0.5 mm. By this arrangement, the heat capacity of eachthermo junction is kept small so that the temperature is accurately andrapidly transformed to a current value. As a result, the temperaturecontrollability is improved and the temperature distribution of thewafer-heating surface is narrowed.

[0134] As examples of said thermocouple, the K, R, B, S, E, J and Tthermocouples as defined in JIS C-1602 (1980) can be mentioned.

[0135] The process for manufacturing a ceramic board for semiconductormanufacture apparatuses according to the present invention is nowdescribed. In the first place, the procedure for fabricating a ceramicboard formed with a conductor layer 12 on the bottom side of a ceramicsubstrate 11, shown in FIG. 1, is described.

[0136] (1) Fabrication of a Ceramic Substrate

[0137] The nitride ceramic powder described above, e.g. an aluminumnitride ceramic powder, is formulated with optional sintering aids, suchas yttria, etc., a binder and other components to prepare a slurry. Thisslurry is granulated by the spray-drying method and the resultinggranules are place in a metal mold or the like and compressed into agreen board.

[0138] Then, the green board is optionally formed with through holes 15for accepting the support pins 16 for supporting a silicon wafer andwith blind holes 14 a to 14 i in which temperature probes such asthermocouples are to be embedded.

[0139] Then, this green board is sintered by heating to provide a blankceramic board. A ceramic substrate 11 is then prepared by machining thisceramic board to predetermined shape. As an alternative, the board maybe formed to the specified size so that it may directly serve as aceramic substrate 11. By conducting a sintering operation underpressure, a pore-free ceramic substrate 11 can be fabricated. Theheating temperature may be any temperature not below the sintering pointbut, in the case of nitride ceramics, the range of 1000 to 2500° C. isused.

[0140] The flatness is adjusted after sintering. The desired flatnesscan be attained by grinding both sides simultaneously using a #100 to#800 (grit size) diamond wheel (two-sided wheel) while a pressure of 0.1to 50 kg/cm² is applied.

[0141] If the grittiness is too small, the surface undulation of theceramic substrate cannot be fully ground off. If the grittiness is toogreat, the very grittiness of the wheel surface rather creates anundulation. The rotational speed of the diamond wheel is 50 to 300 rpm.

[0142] The diamond wheel is prepared by electrodeposition of diamond.

[0143] When both sides are ground concurrently, the grinding stresstends to cause a slight warp in the ceramic substrate, making itdifficult to provide for a flatness of less than 1 μm. To assure aflatness of less than 1 μm, only one side is ground under dead load.

[0144] (2) Printing the Ceramic Substrate With a Conductor Paste

[0145] The conductor paste is generally a highly viscous fluidcomprising a metal powder, a resin and a solvent. The conductor pastelayer is formed by printing the substrate in the areas corresponding tothe conductor layer with said conductor paste by the screen printingtechnique, for instance. Since the conductor layer is required to heatthe ceramic substrate uniformly over its whole surface, it is preferablyprinted in a concentric circular pattern as illustrated in FIG. 1.

[0146] It is preferable that the conductor paste layer be formed in sucha manner that the conductor layer 12 after baking will present arectangular section and a flat surface.

[0147] (3) Sintering the Conductor Paste

[0148] The conductor paste layer formed on the bottom surface of theceramic substrate 11 is then heated and sitered to remove the resin andsolvent and bake the metal powder onto the bottom surface of the ceramicsubstrate 11 to complete a conductor layer 12. The heating temperatureis preferably 500 to 1000° C.

[0149] When said metal oxide has been incorporated in the conductorpaste, the metal powder, ceramic substrate and metal oxide areintegrally sintered to provide an improved bond between the conductorlayer and ceramic substrate.

[0150] (4) Formation of a Metal Cover Layer

[0151] The surface of the conductor layer 12 is preferably provided withthe metal cover layer. The metal cover layer can be formed by, forexample, electrolytic plating, electroless plating or sputtering but,for mass production, electroless plating is the most suitable method.

[0152] (5) Attaching Terminals etc.

[0153] To ends of each circuit pattern of the conductor layer (heatingelement) 12, terminals (terminal pins 13) for electrical connection to apower source are attached by soldering. In addition, thermocouples areset in the blind holes 14 a to 14 i and sealed with a ceramic and aheat-resistant resin such as a polyimide resin to complete themanufacture of a ceramic board having a conductor layer on the bottomside.

[0154] The method of manufacturing a ceramic board having a conductorlayer 12 formed internally of a ceramic substrate is now described.

[0155] (1) Fabrication of a Ceramic Substrate

[0156] First, the nitride ceramic powder is mixed with then binder,solvent, etc. to prepare a paste, and using the paste a green sheet isformed.

[0157] The ceramic powder which can be used includes an aluminum nitridepowder, and where necessary, sintering aids such as yttria may be added.

[0158] The binder is preferably at least one member selected from thegroup consisting of acrylic binder, ethylcellulose, butylcellosolve andpolyvinyl alcohol.

[0159] The solvent is preferably at least one member selected from thegroup consisting of α-terpineol and glycol.

[0160] The paste obtained by compounding those components is molded bythe doctor blade method to provide said green sheet.

[0161] The preferred thickness of the green sheet is 0.1 to 5 mm.

[0162] Then, where necessary, the green sheet is formed with means toserve as through holes for accepting support pins for supporting asilicon wafer, means to serve as blind holes in which temperature probessuch as thermocouples are to be embedded, and means for serving asplated-through holes for connecting the conductor layer to externalterminal pins. This processing may be carried out after formation of agreen sheet laminate to be described below.

[0163] (2) Printing the Green Sheet with the Conductive Paste

[0164] On the green sheet, the conductive paste containing a metal orconductive ceramic powder is printed.

[0165] The conductive paste contains a metal or conductive ceramicpowder.

[0166] The mean particle diameter of tungsten or molybdenum powder ispreferably 0.1 to 5 μm. If the mean particle diameter is less than 0.1μm or over 5 μm, the conductive paste will hardly be printed.

[0167] The conductive paste may for example be a composition (paste)composed of 85 to 87 weight parts of a metal or conductive ceramicpowder, 1.5 to 10 weight parts of at least one kind of binder selectedfrom the group consisting of acrylic binder, ethylcellulose,butylcellosolve and polyvinyl alcohol, and at least one kind of solventselected from the group consisting of α-terpineol and glycol.

[0168] (3) Laminating Green Sheets

[0169] The green sheets not printed with the conductive paste arelaminated on both sides of the green sheet printed with the conductivepaste.

[0170] In this step, it is arranged so that the number of green sheetsto be laminated on the top side is larger than the number of greensheets to be laminated on the bottom side so that the conductor layerwill be situated offset in the direction of the bottom side.

[0171] Specifically, the preferred number of green sheets laminated is20 to 50 on the top side and 5 to 20 on the bottom side.

[0172] (4) Sintering the Green Sheet Laminate

[0173] The green sheet laminate is hot-pressed to sinter the greensheets and the conductive paste within the laminate.

[0174] The heating temperature is preferably 1000 to 2000° C. and thepressure to be applied is preferably 100 to 200 kg/cm². The heating isperformed in an inert gas atmosphere. The inert gas may for example beargon gas or nitrogen gas.

[0175] The blind holes for accepting temperature probes may be formedafter this sintering operation. The blind holes can be formed byblasting, e.g. sandblasting, after surface grinding. In addition,terminals are connected to the plated-through holes for electricalconnection to the internal conductor layer, followed by heating forreflow. The heating temperature is preferably 200 to 500° C.

[0176] The flatness is adjusted after sintering. The desired flatnesscan be attained by grinding both sides simultaneously using a #100 to#800 (grit size) diamond wheel (two-sided wheel) while a pressure of 0.1to 50 kg/cm² is applied.

[0177] If the grittiness is too small, the surface undulation of theceramic substrate cannot be fully ground off. If the grittiness is toogreat, the very grittiness of the wheel surface rather creates anundulation. The rotational speed of the diamond wheel is 50 to 300 rpm.

[0178] The diamond wheel is prepared by electrodeposition of diamond.

[0179] When both sides are ground concurrently, the grinding stresstends to cause a slight warp in the ceramic substrate, making itdifficult to provide for a flatness of less than 1 μm. To assure aflatness of less than 1 μm, only one side is ground under dead load.

[0180] Then, the thermocouples as temperature probes are sealed with aheat-resistant resin to complete a ceramic board internally providedwith a conductor layer.

BEST MODE FOR CARRYING OUT THE INVENTION

[0181] The present invention is now described in further detail.

Example 1 (Manufacture of a Ceramic Board Internally Provided with aConductor Layer)

[0182] (1) A paste prepared by compounding 100 weight parts of aluminumnitride powder (manufactured by Tokuyama Co.; average part. dia.: 1.1μm), 4 weight parts of yttria (average part. dia.: 0.4 μm), 11.5 weightparts of acrylic binder, 0.5 weight part of dispersant and 53 weightparts of alcohol comprising 1-butanol and ethanol was molded by thedoctor blade method to prepare a 0.47 mm-thick green sheet.

[0183] (2) This green sheet was dried at 80° C. for 5 hours and, then,punched to form openings corresponding to through holes for acceptingsilicon wafer-supporting pins (1.8 mm, 3.0 mm and 5.0 mm in diameter)and openings corresponding to plate-through holes for connection toterminal pins.

[0184] (3) A conductor paste A was prepared by compounding 100 weightparts of a tungsten carbide powder having an average particle diameterof 1 μm, 3.0 weight parts of acrylic binder, 3.5 weight parts of thesolvent α-terpineol, and 0.3 weight part of dispersant.

[0185] A conductor paste B was also prepared by compounding 100 weightparts of a tungsten powder having an average particle diameter of 3 μm,1.9 weight parts of acrylic binder, 3.7 weight parts of the solventα-terpineol, and 0.2 weight part of dispersant.

[0186] The above conductive paste A was printed on the green sheet byscreen printing to form a conductor paste layer 104. The printingpattern was a concentric circular pattern as shown in FIG. 1. Inaddition, said through holes corresponding to plated-through holes forconnecting terminal pins were filled with said conductor paste B.

[0187] The green sheet processed above was laminated with 37 units ofthe green sheet not printed with the tungsten paste on the top side(heating side) and 13 units of the same unprinted green sheet on thebottom side at 130° C. under a pressure of 80 kg/cm² (FIG. 3(a)).

[0188] (4) The resulting laminate was degreased in a nitrogen gasatmosphere at 600° C. for 5 hours and hot-pressed at 1890° C. and 150kg/cm² for 3 hours to give a 3 mm-thick aluminum nitride blank board.From this blank board, a 215 mm (dia.) disk was cut out to obtain a0%-porosity ceramic disk internally provided with a 6 μm thick×10 mmwide conductor layer.

[0189] (5) The disk obtained above in (4) was ground on both sidessimultaneously with a double-surface grinder using a #220 diamond wheelat 100 rpm while a pressure of 1 kg/cm² was applied. As a result, aceramic board 111 internally provided with a 6 μm-thick×10 mm-wideconductor layer 102 was obtained (FIG. 3(b)).

[0190] (6) Then, the plated-through holes were partially bored to formrecesses (FIG. 3(c)) and terminal pins 120 comprising Koval® weresecured in the recesses with a Ni—Au brazing material heated to reflowat 700° C. (FIG. 3(d)). Then, blind hole 122 (diameter: 1.2 mm, depth:2.0 mm) were drilled. In addition, a plurality of thermocouples 121 fortemperature control were embedded in the blind holes 122 to complete themanufacture of a ceramic board equipped with a heating elementfunctioning as a conductor layer (FIG. 3(e)).

[0191] The flatness of the wafer-mounting (heating) surface of thisceramic board was 15.5 μm in the X-direction and 12.4 μm in theY-direction over a measurement range of 205 mm [diametric end-to-endlength (215 mm)−10 mm=205 mm]. FIG. 3 is a diagrammatic representationof measurement results, where (a) represents the data in the X-directionand (b) represents the data in the Y-direction.

[0192] The above measurement of flatness was carried out using a warptester (manufactured by Kyocera; Nanoway®). The measurements of flatnessreferred to below were also made with the same instrument.

TEST EXAMPLE 1 (Manufacture of a Ceramic Board Internally Provided Witha Conductor Layer)

[0193] Except that diamond grinding was not performed, the procedure ofExample 1 was otherwise repeated to provide a ceramic board.

[0194] The flatness of the wafer-mounting surface of this ceramic boardwas 25.5 μm in the X-direction and 23.4 μm in the Y-direction over themeasurement length of 205 mm.

COMPARATIVE EXAMPLE 1 (Manufacture of a Ceramic Board InternallyProvided with a Conductor Layer)

[0195] A ceramic substrate was fabricated in the same manner as inExample 1 and, then, subjected to the following diamond grinding.

[0196] Using a grinder having a #220 diamond wheel, only one side of theceramic substrate was ground at 100 rpm under no-load (dead load).

[0197] The flatness of the wafer-mounting surface of the resultingceramic board was 0.55 μm in the X-direction an 0.84 μm in theY-direction over a measurement range of 205 mm.

TEST EXAMPLE 2

[0198] Except that the diameter of the substrate was set to 190 mm andthe substrate was not ground, the procedure of Example 1 was otherwiserepeated to provide a ceramic board.

[0199] The flatness of the wafer-mounting surface of this ceramic boardwas 25 μm in the X-direction and 23 μm in the Y-direction over ameasurement range of 180 mm.

COMPARATIVE EXAMPLE 2

[0200] Except that a ceramic disk to be rejected after hot-pressing wasused, the procedure of Example 1 was otherwise repeated to provide aceramic board.

[0201] The flatness of the wafer-mounting surface of this ceramic boardwas 55 μm in the X-direction and 52 μm in the Y-direction over ameasurement range of 205 mm.

EXAMPLE 2 (Manufacture of a Ceramic Board Provided with a ConductorLayer on the Surface)

[0202] (1) A composition prepared by compounding 100 weight parts ofaluminum nitride powder (manufactured by Tokuyama Co.; average part.dia.: 1.1 μm), 4 weight parts of yttria (averate part. dia.: 0.4 μm) and1 weight part of acrylic binder was placed in a mold and hot-pressed at1890° C. and 150 kg/cm² for 3 hours to provide a sintered aluminumnitride blank board.

[0203] From this sintered aluminum nitride blank board, a 215 mm (dia.)disk was cut out and its surfaces were ground with a double-surfacegrinder using a #220 diamond wheel under a pressure of 1 kg/cm².

[0204] (2) The bottom surface of the sintered compact obtained above in(1) was printed with a conductor paste by screen printing. The printingpattern was a concentric circular pattern as shown in FIG. 1.

[0205] The conductor paste used was Solvest PS603D available fromTokuriki Kagaku Kenkyusho, which is used in the formation ofplated-through holes in printed circuit boards.

[0206] This conductor paste is a silver-lead paste containing, based on100 weight parts of silver, 7.5 weight parts of metal oxide comprisinglead oxide (5 wt. %), zinc oxide (55 wt. %), silica (10 wt. %), boronoxide (25 wt. %) and alumina (5 wt. %). The silver powder had an averageparticle diameter of 4.5 μm and constituted flaky particles.

[0207] (3) The above sintered compact printed with the conduct or pastewas heated at 780° C. to sinter the silver and lead in the conductorpaste and bake them onto the sintered compact to form a heating element12. This silver-lead heating element 12 was 5 μm thick×2.4 mm wide andhad an area resistivity of 7.7 mΩ/□.

[0208] (4) The sintered compact prepared above in (3) was dipped in anelectroless nickel plating bath comprising an aqueous solutioncontaining nickel sulfate: 80 g/l, sodium hypophosphite: 24 g/l, sodiumacetate: 12 g/l, boric acid: 8 g/l and ammonium chloride: 6 g/l todeposit a 1 μm-thick metal cover layer (nickel layer) on the surface ofthe silver-lead heating element 12.

[0209] (5) In the regions where terminals for connection to a powersource are to be attached, a silver-lead soldering paste (manufacturedby Tanaka Noble Metals) was applied by screen printing to form a solderlayer.

[0210] Then, terminal pins 13 comprising Koval® were set on the solderlayers and connected to the surface of the heating element 12 by heatingfor reflow at 420° C.

[0211] The flatness of the heating surface (wafer-mounting surface) ofthe ceramic board thus obtained was 20 μm in the X-direction and 18 μmin the Y-direction over a measurement length of 205 mm.

[0212] (6) Thermocouples for temperature control were set in the blindholes 14 and sealed with a polyimide resin cured at 190° C. for 2 hoursto provide a ceramic heater 10 (FIG. 2).

[0213] This ceramic heater 10 is used in such a manner that, as shown inFIG. 2, a wafer 19 to be heated is supported with support pins 16 set inthe through holes 15 of the ceramic substrate 11 at a distance of 50 μmfrom the ceramic substrate and heated to 250 C. The preferred clearancebetween the ceramic substrate and the wafer is 5 to 500 μm. When theclearance is too large or too small, the temperature distributionbecomes uneven.

COMPARATIVE EXAMPLE 3

[0214] Except that a ceramic disk rejected after hot-pressing was usedand no diamond grinding was performed, the procedure of Example 2 wasotherwise repeated to provide a ceramic board.

[0215] The flatness of the wafer-mounting surface of this ceramic boardwas 55 μm in the X-direction and 60 μm in the Y-direction over ameasurement length of 205 mm.

COMPARATIVE EXAMPLE 4

[0216] Except that only one side of the substrate was ground with a #220diamond wheel at 100 rpm under no-load (dead load), the procedure ofExample 2 was otherwise repeated to provide a ceramic board.

[0217] The flatness of the wafer-mounting surface of this ceramic boardwas 0.45 μm in the X-direction and 0.65 μm in the Y-direction over ameasurement length of 205 mm.

TEST EXAMPLE 3

[0218] Except that no diamond grinding was performed, the procedure ofExample 2 was otherwise repeated to provide a ceramic board.

[0219] The flatness of the wafer-mounting surface of this ceramic boardwas 23 μm in the X-direction and 22 μm in the Y-direction over ameasurement length of 205 mm.

[0220] On each of the ceramic boards obtained in Examples 1 and 2, TestExamples 1 to 3 and Comparative Examples 1 to 4, a silicon wafer wasmounted and the conductor layer (heating element) was supplied with acurrent to increase the heater temperature to 600° C. Then, thedifference between the highest and lowest temperatures of the siliconwafer was measured with a thermoviewer. The difference values were 9° C.for Example 1, 25° C. for Test Example 1, and 9° C. for Test Example 2.In Comparative Example 1, the silicon wafer could not be neatly releasedand, when forced to release, the wafer was damaged. In the case ofComparative Example 2, the temperature rose only to 200° C.

[0221] In the case of Example 2, the temperature difference was 1. Inthe case of Comparative Example 3, the wafer could not be held apart by50 μm, for the wafer would have contacted the ceramic board. In the caseof Comparative Example 4, the silicon wafer could not be released fromthe ceramic board. In the case of Test Example 3, the temperaturedifference of the wafer was 5° C.

Example 3 (Manufacture of an Electrostatic Chuck)

[0222] (1) A paste prepared by compounding 100 weight parts of aluminumnitride powder (manufactured by Tokuyama Co.; average part. dia.: 1.1μm), 4 weight parts of yttria (average part. dia.: 0.4 μm), 11.5 weightparts of acrylic binder, 0.5 weight part of dispersant and 53 weightparts of alcohol comprising 1-butanol and ethanol was molded by thedoctor blade method to provide a 0.47 mm thick green sheet.

[0223] (2) This green sheet was dried at 80° C. for 5 hours.

[0224] (3) A conductor paste A was prepared by compounding 100 weightparts of a tungsten carbide powder with an average particle diameter of1 μm, 3.0 weight parts of acrylic binder, 3.5 weight parts of thesolvent α-terpineol and 0.3 weight part of dispersant.

[0225] A conductor paste B was similarly prepared by compounding 100weight parts of a tungsten powder with an average particle diameter of 3μm, 1.9 weight parts of acrylic binder, 3.7 weight parts of the solventα-terpineol and 0.2 weight part of dispersant.

[0226] The conductive paste A was pattern-printed on the green sheet byscreen printing to form an electrode pattern comprising comb-shapedstatic electrodes and a grid-shaped RF electrode.

[0227] The green sheet processed as above was laminated with 37 units ofthe green sheet not printed with the tungsten paste on the top side(heating side) and 13 units of the same unprinted green sheet on thebottom side at 130° C. and 80 kg/cm².

[0228] (4) The resulting laminate was degreased in a nitrogen gasatmosphere at 600° C. for 5 hours and hot-pressed at 1890° C. and 150kg/cm² for 3 hours to prepare a 3 mm-thick aluminum nitride blank board.From this blank board, a 215 mm (dia.) disk was cut out and ground witha diamond wheel as in Example 1 to provide a ceramic board(electrostatic chuck) internally provided with a conductor layer 6 μmthick×10 mm wide.

[0229] The flatness of the wafer-mounting (heating) surface of thisceramic board was 8.2 μm in the X-direction and 4.5 μm in theY-direction over the measurement range of 205 mm. FIG. 4 is adiagrammatic representation of measurement results, where (a) representsdata in the X-direction and (b) represents data in the Y-direction.

TEST EXAMPLE 4 (Manufacture of an Electrostatic Chuck)

[0230] Except that diamond grinding was not performed, the procedure ofExample 3 was otherwise repeated to provide an electrostatic chuck.

[0231] The flatness of the wafer-mounting (heating) surface of thiselectrostatic chuck was 25.5 μm in the X-direction and 23.4 μm in theY-direction over a measurement range of 205 mm.

COMPARATIVE EXAMPLE 5 (Manufacture of an Electrostatic Chuck)

[0232] An aluminum nitride board was prepared as in Example 3 and groundwith a diamond wheel as in Comparative Example 1 to provide anelectrostatic chuck.

[0233] The flatness of the wafer-mounting surface of this electrostaticchuck was 0.55 μm in the X-direction and 0.84 μm in the Y-direction overa measurement range of 205 mm.

TEST EXAMPLE 5

[0234] Except that the diameter of the ceramic disk was set to 190 mmand the disk was not ground, the procedure of Example 3 was otherwiserepeated to provide an electrostatic chuck.

[0235] The flatness of the wafer-mounting (heating) surface of thiselectrostatic chuck was 26 μm in the X-direction and 25 μm in theY-direction over a measurement range of 180 mm.

COMPARATIVE EXAMPLE 6

[0236] Except that a ceramic board rejected after hot-pressing was used,the procedure of Example 3 was otherwise repeated to provide anelectrostatic chuck.

[0237] The flatness of the wafer-mounting (heating) surface of thiselectrostatic chuck was 55 μm in the X-direction and 52 μm in theY-direction over a measurement range of 205 mm.

[0238] Then, to evaluate the chucking forces of the electrostatic chucksmanufactured as above, a voltage of 1 kV was applied to each chuck toattract a silicon wafer and the force required to release the wafer wasmeasured by means of a load cell. As a result, the releasing forcerequired in a vacuum was 125 g/cm² in the case of the electrostaticchuck according to Example 3 and 80 g/cm² in the case of theelectrostatic chuck according to Test Example 4. With the electrostaticchuck according to Comparative Example 5, the silicon wafer becameunreleasable when the atmospheric pressure was reinstated and, whenforced to release it, the wafer was damaged. In the case of theelectrostatic chuck according to Test Example 5, the releasing forcerequired was 110 kg/cm². As to the electrostatic chuck according toComparative Example 6, the wafer cracked when a voltage of 1 kV wasapplied to the chuck to measure the force of attraction.

EXAMPLE 4 (Manufacture of a Wafer Prover)

[0239] (1) A composition prepared by compounding 100 weight parts ofaluminum nitride powder (manufactured by Tokuyama Co.; average part.dia.: 1.1 μm), 4 weight parts of yttria (average part. dia.: 0.4 μm),11.5 weight parts of acrylic binder, 0.5 weight part of dispersant and53 weight parts of alcohol comprising 1-butanol and ethanol was moldedby the doctor blade method to provide a 0.47 mm-thick green sheet.

[0240] (2) This green sheet was dried at 80° C. for 5 hours and punchedto pierce through holes for use as plated-through holes for connecting aheating element to external terminal pins.

[0241] (3) A conductive paste A was prepared by compounding 100 weightparts of a tungsten carbide powder with an average particle diameter of1 μm, 3.0 weight parts of acrylic binder, 3.5 weight parts of thesolvent α-terpineol, and 0.3 weight part of dispersant.

[0242] Similarly, a conductive paste B was prepared by compounding 100weight parts of a tungsten powder with an average particle diameter of 3μm, 1.9 weight parts of acrylic binder, 3.7 weight parts of the solventα-terpineol, and 0.2 weight part of dispersant.

[0243] Then, using the conductive paste A, a grid-shaped guard electrodepattern 50 and a ground electrode pattern 60 were printed on the greensheet by screen printing.

[0244] In addition, the through holes for the plated-through holes forconnecting terminal pins were filled with the conductive paste B.

[0245] Then, this printed green sheet 30 was laminated with 50 units ofthe unprinted green sheet 30 at 130° C. and 80 kg/cm² to provide alaminate (FIG. 6(a)).

[0246] (4) This laminate was degreased in a nitrogen gas atmosphere at600° C. for 5 hours and hot-pressed at 1890° C. and 150 kg/cm² for 3hours to provide a 3 mm-thick aluminum nitride blank board From thisblank board, a 215 mm (dia.) disk was cut out (FIG. 6(b)). The size ofplated-through holes 26, 27 was 0.2 mm in diameter and 0.2 mm deep.

[0247] The thickness of said guard electrode 5 and ground electrode 6was 10 μm. The position of the guard electrode 5 was 1 mm from thewafer-mounting surface and the position of the ground electrode 6 was1.2 mm from the wafer-mounting surface.

[0248] (5) The disk obtained above in (4) was ground with a diamondwheel as in Example 1 and, with a mask set in position, cavities foraccepting thermocouples (not shown) and grooves 7 (0.5 mm wide×0.5 mmdeep) for attracting a silicon wafer were formed by SiC blasting (FIG.6(c)).

[0249] (6) Then, a heating element 41 was printed on the surfaceopposite to the wafer-mounting surface. This printing was made with aconductor paste. The conductor paste used was Solbest PS603Dmanufactured by Tokuriki Kagaku Kenkyusho, which is used in theformation of plated-through holes in printed circuit boards. Thisconductor paste contained, based on 100 weight parts of silver, 7.5weight parts of metal oxide composed of lead oxide, zinc oxide, silica,boron oxide and alumina (5/55/10/25/5, by weight).

[0250] The silver powder used had an average particle diameter of 4.5 μmand constituted flaky particles.

[0251] (7) The heater plate printed with the conductive paste as abovewas heated at 780° C. to sinter the silver and lead in the paste andbake them onto the ceramic substrate 3 to form a heating element 41(FIG. 6(d)). This heater plate was then dipped in an electroless platingbath comprising an aqueous solution containing nickel sulfate: 30 g/l,boric acid: 30 g/l, ammonium chloride: 30 g/l and Rochelle salt: 60 g/lto deposit a 1 μm-thick nickel layer 410 (boron content≦1 wt. %) on thesurface of the sintered silver heating element 41. Thereafter, theheater plate was annealed at 120° C. for 3 hours.

[0252] The heating element of sintered silver was 5 μm thick×2.4 mm wideand had an area resistivity of 7.7 mΩ/□.

[0253] (8) On the surface formed with grooves 7, a titanium layer, amolybdenum layer and a nickel layer were serially constructed bysputtering. As the sputtering equipment, SV-4540 manufactured by JapanVacuum Technology Co. was used. The sputtering conditions were 0.6 Pa,100° C. and 200 W and the sputtering time was adjusted according to thekind of metal within the range of 30 seconds to 1 minute.

[0254] The thickness of each metal film according to the image output ofa fluorescent X-ray analyzer was the titanium layer: 0.3 μm, themolybdenum layer: 2 μm, and the nickel layer: 1 μm.

[0255] (9) Using an electroless nickel plating bath comprising anaqueous solution of nickel sulfate: 30 g/l, boric acid: 30 g/l, ammoniumchloride: 30 g/l and Rochelle salt: 60 g/l and an electrolytic nickelplating bath containing nickel sulfate: 250 to 350 g/l, nickel chloride:40 to 70 g/l, and boric acid: 30 to 50 g/l and adjusted to pH 2.4 to 4.5with sulfuric acid, the ceramic substrate obtained in (8) was dipped todeposit a 7 μm-thick nickel layer (boron content≦1 wt. %) on the surfaceof the above metal layer formed by sputtering and the substrate was thenannealed at 120° C. for 3 hours.

[0256] The surface of the heating element, which was not electricallyconductive, was not plated by the electrolytic nickel plating.

[0257] Then, the board was dipped in an electroless gold plating bathcontaining potassium gold cyanide: 2 g/l, ammonium chloride: 75 g/l,sodium citrate: 50 g/l and sodium hypophosphite: 10 g/l at 93° C. for 1minute to form a 1 μm-thick gold layer on the nickel plate (FIG. 7(e)).

[0258] (10) Air suction holes 8 extending from the grooves 7 to thereverse side were formed by drilling, and recesses 28 for exposing theplated-through holes 26, 27 were formed (FIG. 7 (f)). In the recesses28, external terminal pins 29, 290 comprising Koval® were secured with aNi—Au brazing alloy (Au: 81.5 wt. %, Ni: 18.4 wt. impurity: 0.1 wt. %)heated for reflow at 970° C. (FIG. 7(g)). Moreover, external terminalpins 291 comprising Koval® were connected to the heating element withthe aid of a solder (tin/lead=9/1).

[0259] (11) Then, a plurality of thermocouples for temperature controlwere embedded in the cavities to obtain a wafer prover. The flatness ofthe wafer-mounting surface of this wafer prover was 15.5 μm in theX-direction and 12.4 μm in the Y-direction over a measurement range of205 mm.

[0260] (12) This wafer prover 101 was set on a stainless steel support31 through a ceramic fiber (manufactured by Ibiden; trade name:Ibi-Wool) insulation 30 as shown in FIG. 8. This support 31 is providedwith a plurality of nozzle ports 32 for ejecting a cooling medium tothereby adjust the temperature of the wafer prover 101. It is alsoprovided with a suction port 33 for aspirating the cooling medium or airto thereby attract the silicon wafer.

Test Example 6 (Manufacture of a Wafer Prover)

[0261] Except that diamond grinding was not performed, the procedure ofExample 4 was otherwise repeated to provide a wafer prover.

[0262] The flatness of the wafer-mounting surface of this wafer proverwas 25.5 μm in the X-direction and 23.4 μm in the Y-direction over ameasurement range of 205 mm.

COMPARATIVE EXAMPLE 7

[0263] Except that a ceramic substrate rejected after hot-pressing wasused, the procedure of Example 4 was otherwise repeated to provide awafer prover.

[0264] The flatness of the wafer-mounting surface of this wafer proverwas 55 μm in the X-direction and 52 μm in the Y-direction over ameasurement range of 205 mm.

[0265] A silicon wafer was mounted on each of the wafer provers obtainedin Example 4 and Test Example 6 and healed. With the wafer proveraccording to Example 4, the silicon wafer was not damaged. With thewafer prover according to Test Example 6, the wafer was destroyed.

[0266] A silicon wafer was mounted on the wafer prover obtained inComparative Example 7 and the temperature was increased to 200° C.However, because the wafer and the prover were in line contact, thewafer temperature failed to rise and the test could not be performed.

[0267] Thus, in accordance with the present invention, wherein theflatness of the wafer-mounting surface is controlled to not more than 50μm, a silicon wafer can be successfully heated. In particular, a uniformwafer temperature can be obtained by controlling the flatness to notmore than 20 μm. Moreover, chucking the work causes no wafer damage.

[0268] The above results are particularly remarkable with disk-shapedceramic boards not less than 200 mm in diameter.

INDUSTRIAL APPLICABILITY

[0269] As described above, the ceramic board for semiconductormanufacture apparatuses according to the present invention, when used asa heater, heats a silicon wafer uniformly throughout and, hence, doesnot damage the wafer and, when used as an electrostatic chuck, providesa sufficient chucking force, thus finding application as implements forsemiconductor manufacture apparatuses, such as the hot plate,electrostatic chuck and wafer prover, with the outstanding advantage.

1-9. (Canceled)
 10. A method for preparing a ceramic board for asemiconductor manufacturing apparatus, where the ceramic board comprisesa ceramic substrate and a conductor layer disposed on a surface of theceramic substrate, the ceramic substrate has a semiconductor wafermounting surface for directly mounting a semiconductor wafer thereon,and the semiconductor wafer mounting surface is controlled to a flatnessof 1 to 50 μm over a measurement area which ranges until a point 10 mmdistant from the diametric end of the semiconductor wafer mountingsurface, wherein the method comprises: mixing a ceramic powder with asolvent, a binder, and optionally a sintering aid, thereby forming aceramic paste; forming a green ceramic sheet from the ceramic paste;heating the green ceramic sheet at a temperature sufficient to sinterthe green ceramic sheet, thereby forming a blank ceramic board;flattening the blank ceramic board; forming a conductor paste comprisinga mixture of a metal or a conductive ceramic powder, a resin, and asolvent; depositing the conductor paste on the surface of the flattenedceramic board; and heating the blank ceramic board upon which theconductor paste has been deposited to a temperature sufficient to sinterthe metal or the conductive ceramic powder of the conductor paste.
 11. Amethod for preparing a ceramic board for a semiconductor manufacturingapparatus, where the ceramic board comprises a ceramic substrate and aconductor layer disposed internally in the ceramic substrate, theceramic substrate has a semiconductor wafer mounting surface fordirectly mounting a semiconductor wafer thereof, and the semiconductorwafer mounting surface is controlled to a flatness of 1 to 50 μm over ameasurement area which ranges until a point 10 mm distant from thediametric end of the semiconductor wafer mounting surface, wherein themethod comprises: mixing a ceramic powder with a binder, a solvent, andoptionally a sintering aid, thereby forming a ceramic paste; forming atleast two green ceramic sheets from the ceramic paste; forming aconductor paste comprising a mixture of a metal or a conductive ceramicpowder, a solvent, and a resin; forming a layer of the conductor pasteon at least one green ceramic sheet; laminating at least two greenceramic sheets together so that the conductor paste layer is disposedbetween two green ceramic sheets; heating the laminated sheets to atemperature sufficient to sinter the green ceramic sheets and theconductor layer; and flattening at least one exterior surface of thelaminated, sintered sheets.